Present-day method of finishing concrete slabs such as are used for road surfaces, utilize a slip forming machine to form the edges, screed and trowel the surface, as well as inserting some of the structural steel. The road is finished, and the concrete permitted to cure before the final testing is done to determine if the surface meets smoothness requirements.
From an early date, wheeled vehicles, called profilographs, have been used to measure the smoothness of a cured road surface, hard enough to support the wheels of the profilograph. Some commonly used varieties of profilographs are the California Profilograph and the Rainhart Profilograph.
The need for a profiler using non-contact sensors was recognized some years ago. A paper entitled Development of a Non-contact Pavement Smoothness Monitor for Use During Construction was prepared for presentation at the 1984 Annual Meeting of the Transportation Research Board by Jeffrey A. Bloom. Described in this paper is a system for determining an aspect of road smoothness using non-contact ultrasonic sensors at four locations arranged along the road surface (parallel to the direction traveled by motor vehicles). The data from the sensors are used to calculate a quantity called Asymmetric Chord Offset (ACO). Using any three sets of sensors, a chord line can be envisioned between the points at which the outer two sets of sensors reflect off the road surface. The set of sensors in between these outer sets of sensors measures a distance between the road surface and the sensor set. The distance between the point on the road surface where this middle signal reflects and the point on the chord line directly below these middle sensor sets is the ACO for those three sets of sensors. Data are taken every three inches (in a direction parallel to traffic). Multiple sets of these sensors are used to make simultaneous measurements at a plurality of locations across the road surface.
With this method, only relative measurements are taken. No absolute datum is compared to, and the locations of the individual sensors relative to the road surface vary as the device moves forward. The slope of the beam on which the sensors are mounted is not measured. Therefore, an elevation profile of the road surface is not possible. Only values of ACO are calculated.
The bank of sensors disclosed in the above mentioned paper are mounted on a four-wheeled vehicle (called a “bridge”), made to straddle the road (the wheels run outside the concrete and forms, if any). Therefore, the operation performed by the apparatus is strictly a measuring and recording operation. Modifications to the surface profile, based on the findings of this measurement, are performed by separate machinery after the measuring step. Adjustments to the road finishing machinery may not be possible in real time. Furthermore, the Jeffrey A. Bloom bridge is a rather large apparatus, making transport difficult.
For the reasons mentioned, there is a need for a method to measure the elevation profile of the surface of a road using non-contact sensors as a device independent of a paving machine. Further need is for a device that can be mounted on a slip form paving machine (or other type of road-surface finishing device), permitting immediate correction to unacceptable surface profiles, as well as adjustments to the finishing machine's operation in real time.